The proposed research is focused on STD transmission within sexual dyads and on factors associated with early subsequent infections (those occurring within one month of initial infection). This focus allows comparison of uninfected with infected dyads, evaluation of factors from each partner associated with within-dyad transmission (assessed at the time of enrollment) and subsequent infection (within one month of initial infection.). Partner agreement on key STD risk and protective behaviors is also assessed. Organisms of interest are N. gonorrhoeae, C. trachomatis and T. vaginalis. Enrollment and evaluation of new partners allows more complete assessment of factors related to early reinfection. In dyads where both members are infected by gonorrhea, concordant opa-types establishes within-dyad transmission. In dyads where both members are infected by chlamydia, identical omp-1 DNA sequences suggests that the source of infection is within-dyad. Discordant opa-type or omp-1 DNA sequence established the source of infection as extra-dyadic. Concordance for trichomonas infection will be assessed by polymerase chain reaction. Overall, the research is expected to provide data of key importance for the implementation of more effective STD screening and treatment programs, especially those focused on high risk adolescents and young adults.